The fourth-placed Milan are on an unbeaten streak of four and could make up further ground on the likes of Sampdoria and Roma with victory at San Siro.
A wretched campaign last term means Milan are free of European commitments this season - something that could play a key role in determining Sunday's outcome.
While Milan will have had a week to prepare for the match, Fiorentina's own continental exertions - which saw them beat PAOK 1-0 on Thursday - leaves them with little time to focus on the Italian giants.
New Milan coach Filippo Inzaghi has his side playing an attacking brand of football - evidenced by the fact they have scored 16 league goals in seven games this term.
No side has more, with Japanese midfielder Keisuke Honda weighing with six of them.
Jeremy Menez has added three and Poli - who said Inzaghi has brought the feel-good factor back to Milan - believes that victory against Fiorentina can really set them up for a big season.
"With commitment, work and desire we can do everything," Poli told Milan Channel.
"Against Fiorentina it will already be a fundamental match.
"There's a positive spirit [in the camp]. After a season like the one last year, it has to be like this.
"We come off the back of a negative year, but there's a desire for revenge and to do well.
"The spirit will take us through this year. We want to continue like this.
"We're now expecting a fundamental match against a very strong rival which has to be approached with the right determination and that will say a lot about us."
Fiorentina sit 11th after a patchy start to the season and lost 2-0 at home to Lazio in their last Serie A match.
While they are flying in the UEFA Europa League, having won all three matches, Fiorentina have struggled to juggle both that and their domestic commitments.
As a result, they have taken just nine points from their first seven matches this season.
Coach Vincenzo Montella will be unhappy with the fact they have scored just five goals in those seven clashes, but will take heart from their impressive recent record at San Siro.
Fiorentina have won on their last two visits to the iconic ground, including a 2-0 success in November last year in which Juan Vargas and Borja Valero netted.
Riccardo Montolivo is likely to miss through injury for Milan, but Nigel de Jong is set to return from suspension.